1. Field of the Invention
This invention relates to a fluorescence observation apparatus used to irradiate a specimen with light and to detect light emanating from the specimen, especially fluorescent light.
2. Description of Related Art
Recently, in biology, researches that use specimens in which a biological function is not retained, but a living condition is maintained has been widely conducted. Specifically, a fluorescent molecule is peculiarly bonded to a remarkable, particular protein molecule, and a fluorescence microscope is used to observe and analyze the behavior and distribution of these molecules so that biological functions are clarified. In addition to this, with the advent of GFP (green fluorescent protein) in recent years, it has become possible to produce fluorescent protein in a cell so that the observation and analysis can be made in a state where more physiological activity is held.
“GFP and bioimaging” (Experiment Medicine, separate volume; Experiment Lecture 3 of Postgenome Age, Yodosha, page 156, 2000) gives the description that it is important that, in order to maintain a state of cellular physiological activity, as an imaging point of a living cell, excitation light for irradiating a specimen is rendered as faint as possible by an attenuation filter and fluorescent light emanating from the specimen is fully utilized, that is, a high-sensitivity fluorescence observation with a high SIN ratio is carried out.
Each of Japanese Patent Kokai Nos. Hei 03-269405, Hei 10-96862, and Hei 10-227980 discloses a technique that aims at a high-sensitivity fluorescence microscope.
The technique disclosed in Kokai No. Hei 03-269405 is such that irradiation light from a light source is converted into annular light and a specimen is irradiated with this light that fails to pass through an objective lens. As an example where an immersion objective lens having a numerical aperture greater than 1.0 is used, the technique disclosed in Kokai No. Hei 10-227980 is known. In the technique disclosed in Kokai No. Hei 10-96862, a reflecting mirror is placed so that part of fluorescent light emanating from a specimen is blocked, and irradiation light from a light source is reflected toward the specimen by this reflecting mirror.